Control system for multiple motor hydraulic means

ABSTRACT

A control system for hydraulic power means incorporating two motors. The control system provides for alternative operation of one motor or of both motors and for transition between one motor and two motor operation without abrupt change and without passing through a neutral condition in which neither mode of operation is in effect.

United States Paten 1191 Ratliff et a1. Nov. 26, 1974 CONTROL SYSTEM FOR MULTIPLE 2,830,784 4/1958 Placette 251/25 x MOTOR HYDRAULIC MEANS 3,344,805 10/1967 Wapner 137/486 3,473,442 10/1969 Farmer 91/412 [75] Inventors: Frank W. Ratliff; James R.

MB tt,b th fC 'th,M' c O O 188 Primary Examiner-Edgar W. Geoghegan [73] Ass1gnee: Tyrone Hydraulics, Inc., C0r1nth, A mm E min -william F Woods Ml$$- Attorney, Agent, or FirmSynnestvedt & Lechner [22] Filed: Dec. 4, 1972 [21] Appl. No.: 311,791 [57] ABSTRACT A control system for hydraulic power means incorpo- [52] [1.5. Cl. 60/483 rating two motors, The ontrol system provides for al- [51] Int. Cl. F16k 39/48 ternative o eration of one motor or of both motors Field of Search and for transition between one motor and two motor 5 91/412 operation without abrupt change and without passing through a neutral condition in which neither mode of [56] References Clted operation is in effect.

UNITED STATES PATENTS 2,370,526 2 1945 Doran 60/483 8 Clams 4 Drawmg F'gures W "fl PATENTEL NUVZB [974 SHEH NF 2 CONTROL SYSTEM FOR MULTIPLE MOTOR HYDRAULIC MEANS FIELD OF THE INVENTION This invention relates to fluid pressure control systems for power means having first and second hydraulic motors both connected to deliver power to a power shaft, the control system providing alternatively for operation of one motor only or for operation of both motors. The equipment of the present invention is especially adapted to employment in load lifting equipment as employed for example, in various winches, for instance in winch drives such as those used on hydraulic cranes.

Although the invention is applicable to various multiple motor hydraulic power systems in which it is desired to provide alternatively for operation of one motor only or for operation of more than one motor, an installation in a winch drive for a crane is typical and such use of the invention is briefly described as an aid to an understanding of the background of the invention.

BACKGROUND OF THE INVENTION In a load handling crane having a winch adapted to lift and lower a hook, it is frequently desirable to make provision for operation of the winch at different speeds, so that raising of the load may, for example, be initiated at a low speed, and then the speed of raising may be increased during a portion of the distance through which the load is lifted, and again, toward the upper end of the lift, it is frequently desirable to reduce the rate of lifting. Similarly it is frequently desirable to have control of the motor displacement, and by employing two motors and a selectively adjustable control system, the displacement may be altered by alternative operation of either one motor or of both motors, as is known. When the available hydraulic operating fluid for the motors is delivered to only one motor, the speed of lifting is increased, but the displacement is decreased, and, conversely when both motors are supplied with operating fluid from source, the speed is decreased, but the displacement is increased. When the displacement is decreased, the pressure is increased, and conversely.

OBJECTS AND ADVANTAGES The present invention is concerned with a system of the general kind above referred to and has as a major objective the provision of a control system which insures a gradual changeover from either condition ofoperation to the other, thereby virtually eliminating abrupt or jolting action in the handling of loads, especially at those times when a transition is made from one condition of operation to the other.

The invention also provides for changeover by means of a selectively controllable valve mechanism which has no neutral or intermediate setting in which neither of the two operating conditions prevails. This is in contrast to certain prior control systems for this general purpose, in which the control valve has a neutral condition which may even permit momentary dropping of the load.

In accordance with still another aspect of the invention, the control system and the various valve devices employed therein are arranged with reference to the motors so that the control system and the motors are reversible, and will provide the desired operating characteristics with either direction of operation of the motors.

BRIEF DESCRIPTION OF THE DRAWINGS How the foregoing objects and advantages are attained together with others which will occur to those skilled in the art will be clear from the following description referring to the accompanying drawings in which FIG. 1 is a sectional view through a multiple motor hydraulic power means of a kind with which the control system of the invention is adapted to be used;

FIG. 2 is a diagram of the control system with two of the valve devices illustrated in section and with the main control valve in the position providing for high speed operation, i.e., operation by only one of the two motors;

FIG. 3 is a fragmentary diagrammatic view of the main control valve shown in FIG. 2, but positioned to provide low speed multiple motor operation; and

FIG. 4 is a fragmentary sectional view of one of the valve devices shown in FIG. 2, but with the valve in a different position as compared with FIG. 2.

DETAILED DESCRIPTION OF THE DRAWINGS Referring first toFIG. 1, the body or enclosure for a hydraulic gear motor is indicated generally by the reference numeral 5. The details of construction of the motor need not be considered herein, but it is pointed out that the motor assembly comprises two motors, the first of which is made up of a pair of meshing gears 6,7 mounted by means of shafts 8 and 9, the latter of which has a projecting end 10 constituting the power output shaft for the system.

The other motor includes a pair of meshing gears 11 and 12 mounted by means of shafts l3 and 14, the latter of which is connected with the shaft 9 of the first motor by means of spline coupling 15.

In a manner already well known, passages are provided at opposite sides of both of the motors, so that the motors may be supplied with the hydraulic operating fluid and so that the fluid may be delivered from the motors and returned to reservoir.

It will be understood that with a motor system such as shown in FIG. I and with an appropriate control system for the hydraulic operating fluid, either the first motor may be operated alone or both of the motors may be operated. A control system for this purpose is diagrammed-in FIG. 2.

The fluid passages at the two sides of each of the two motors communicate with two valve devices which are advantageously incorporated in the body 5 of the motor itself. These valve devices are not shown in FIG. 1, but are illustrated in section in FIG. 2 in positions facilitating the diagrammatic representation of the control system-shown in FIG. 2. The two valve devices are illustrated generally in FIG. 2 by the reference numerals l6 and 17, the former also being shown in FIG. 4, but with the valve in a different position.

Although, the various partsof the control system are symmetrically arranged with respect to each other and with respect to the motors, so that the system and the motors may be operated in either direction, for simplicity in the initial description of the control system, it is here assumed that the valve device 16 is serving as the supply valve for the motors and that the valve device 17 is serving as the discharge valve for the motors. This condition is established by positioning of the reversing valve R in the position in which the section of the valve indicated at R3 is in position to cooperate with the supply and discharge lines connected with the reversing valve. This is the condition shown in FIG. 2.

In the illustration of the valve 16 in FIG. 2, the passages 18 and 19 respectively represent the supply passages for the first and second motors which are diagrammatically represented at M-1, M-2 in FIG. 2. The

power output connection and the spline coupling between the two motors are also diagrammatically indi-' cated in FIG. 2.

In the valve device 16 there are two cavities 20 and 21 which are respectively connected with the motor passages 18 and 19 and which are adapted to be interconnected by the port 22 having a valve seat 23 with which the poppet valve 24 cooperates, so that the cavities 20 and 21 and thus the passages 18 and 19 may be either separated or interconnected according to the position of the valve 24.

A pump 25 deriving hydraulic fluid from the reservoir 26 communicates with the pasage 18 and thus with cavity 20 through connection 27, the reversing valve R, and connection 27a. The connection 28 which may be arranged internally of the body 5 delivers operating fluid to the inlet side of the motor M-1, and it will be noted that this delivery will be maintained regardless of the position of the valve 24. When the valve 24 is open operating fluid will pass from the cavity 20 through the port 22 into the cavity 21 and thus to the inlet side of the second motor as by the passage 29, which, again may be located internally of the body 5 ofthe motor assembly.

In the condition represented by FIG. 2 the valve device l7 at the left of the Figure occupies the position of the discharge valve for the motors, and here it will be seen that the motor passages 30 and 31 communicate with cavities 32 and 33 having an interconnecting port 34 with a seat 35 adapted to be controlled by a valve 36. Passages formed internally of the motor body 5 include the passage 37 from the first motor to the cavity 32 and passage 30, and passage 38 from the second motor to the passage 31 and cavity 33. An external connection 39a extends to the reversing valve R and communicates with connection 39, thereby providing for delivery of operating fluid from the passage 30 and thus from the cavity 32 of the valve 17 back to reservoir as indicated at 26. It will be seen that fluid discharging from the motor M-l passes directly to reservoir regardless of the position of valve 36 and further that when the valve 36 is open fluid may be discharged from both motors and returned to reservoir through the connection 39a and 39.

The control system also includes a primary manually operated control valve indicated generally at 40, and this valve is shown in FIG. 2 in the position providing for high speed operation, i.e., operation ofonly the first motor indicated at M-l in FIG. 2. In explaining the operation of this manual control valve attention is now directed to the fact that each of the valve devices 16 and 17 includes a piston 41 and 42 connected respectively with the poppet valves 24 and 36 and serving to seat and unseat the poppet valves. Behind piston 41 is a chamber 43 and behind piston 42 is a chamber 44, these chambers comprising pressure fluid chambers serving, in cooperation with the springs 45 and 46, to control the motion of the pistons 41 and 42 and thus of the poppet valves 24 and 26. 36.

Chamber 43 has a port 47 communicating with a discharge pipe 48 through a branch 48a. Similarly chamber 44 has a port 49 communicating with the discharge pipe 48 through a branch 48!). Branch 48a has a restricted port or orifice 50 and a similar orifice 51 is provided in the branch 48b. These two branches also have check valves 52 and 53, the check valve 52 permitting free flow of fluid from the chamber 43 to the discharge pipe 48 but preventing reverse flow, and the check valve 53 permitting free flow of fluid from the chamber 44 to the discharge pipe 48 but preventing reverse flow.

As shown, a discharge pipe 54 has two branches 54a and 54b which are extended respectively to the cavities 21 and 33 in the valve devices 16 and 17. The interconnection between the discharge pipe 54 and its branches 54a and 54b comprises a double acting check valve indicated at 55, which valve serves to permit flow of pressure fluid from cavity 21 or cavity 33 to-the discharge pipe 54 and to prevent flow in either direction between the cavities 21 and 33.

The two discharge pipes 48 and 54 extend to the main control valve 40 and in accordance with the position of that valve, one or the other of the discharge pipes is connected with the return line 56 extended to reservoir, as is indicated. In the position of the main control valve 40 shown in FIG. 2, the discharge pipe 48 is shut off, but the discharge pipe 54 is connected through passage 57 with the return line 56. With the position of the main control valve 40 as shown in FIG. 3, the discharge pipe 54 is closed and the discharge pipe 48 is connected with the return line 56 through the passage 58.

Before describing the operation of the control system attention is further called to the restricted port 59 which extends through the base of the cylinder 41 of the valve device 16, and interconnects the chamber 43 with the cavity 20. Similarly in the piston 42 of the valve device 17 a restricted port 60 interconnects the chamber 44 with the cavity 32.

Each of the valves 24 and 36 is also provided with a peripherally notched portion, respectively indicated at 61 and 62, and serving as metering grooves for the flow of hydraulic fluid from the cavity 20 or 32, to the cavity 21 or 33 while the respective valves are in transition (opening or closing). These passages contribute to the smoothness of shift, when the control system is adjusted to change the mode of operation from single motor to two motor operation or from two motor operation to single motor operation. It is to be noted that in FIG. 4 the control valve 24 is shown part-way open. The opening movement will normally continue until the rear end of the piston 41 abuts against the closure cap, at which time the grooved portion 61 of the valve will be displaced somewhat to the right of the valve seat 23. At that time pressure fluid will flow freely from the chamber 20 into the chamber 21, without the restriction provided by the metering grooves. Thus it will be seen that the metering grooves are effective only throughout the opening or closing portion of the stroke of the piston. The valve at the other side of the system, being symmetrical with the one just described will also function in a similar manner with respect to the operation of the metering grooves 62.

In the setting of the main control valve shown in FIG. 2, with the hydraulic fluid being supplied from the pump through connections 27 and 27a to the passage 18 and cavity 20, the operating fluid is delivered through the passage 28 to the first motor, and the discharge from the first motor occurs through the connection 37, the cavity 32, passage 30 and the discharge pipes 39a and 39. In this condition any pressure fluid present in cavities 21 and 33, passages 19 and 31, and connections 29 and 38 which extend to the second motor may all be freely discharged through the discharge pipe 54, the valve passage 57 and the return line 56. In addition since the discharge pipe 48 is closed at the valve 40, pressure cannot bleed away from the control chambers 43 and 44, and pressure will be maintained in those chambers by virtue of flow of pressure fluid through the restricted ports 59 and 60. This pressure in the chambers 43 and 44, in combination with the action of the springs 45 and 46 and in combination with larger areas in chambers 43 and 44 will assure that the poppet valves 24 and 36 will remain seated, isolating the second motor.

When the control valve 40 is moved to the position shown in FIG. 3, the pressure in chambers 43 and 44 will bleed away through the branch pipes 48a and 48b and the discharge pipe 48, and because of the presence of substantial piston area in the cavities 20 and 32, and differential pressure across orifices 59 and 60, a net force causes the pistons 41 and 42 to be moved against the action of springs and 46, thereby unseating the poppet valves 24 and 36. This will result in flow of hydraulic operating fluid from cavity 20 into cavity 21 and from there to the inlet side of the second motor. Similarly the opening of the valve 36 will result in discharge of the operating fluid from the second motor through passage 31, cavity 33, cavity 32 and the return line 39. In this condition, therefore, both motors will operate.

This condition with both motors operating, requires that the pressure in chambers 43 and 44 be maintained at a relatively low value. For this purpose the restricted passages 59 and 60 should not be substantially larger than the restrictions and 51. To assure that the pressure in the control chambers 43 and 44 will remain relatively low and thus assure that the poppet valves 24 and 36 will remain open when the discharge line 48 is open, the restricted passages 59 and are preferably somewhat smaller than the restrictions 50 and 51.

The restricted ports 59 and 60 and also the restricted orifices 50 and 51, aid in providing changeover from either operating condition to the other without abrupt transition. The metering grooves 61 and 62 are also important in providing against abrupt transition between the two conditions of operation.

When the control system is adjusted to change from the condition where both motors are operating to the condition where only the first motor is operating, the initial revolution of the gears of the second motor will expel the liquid from that motor, discharging such liquid through the branch 54b and the discharge pipe 54 to the return line 56, and thereafter the second motor will turn or run starved. Thus, in this condition the second motor is not even circulating hydraulic fluid. This is a desirable feature of the system of the present invention, because even the idle circulation of hydraulic liquid represents a power loss. Although certain other expedients may be relied upon for this purpose (for instance leakage in the motor itself) the provision of the discharge pipe 54 with its branches 54a and 54b is an effective and reliable system which is readily adaptable to either direction of operation of the mo tors.

Turning again to FIG. 2 and the action of the reversing valve R, it is first to be noted that the symmetry of the control system is of advantage in permitting the entire system including the motors to operate in either direction. Such reversal in operation is effected by means of the reversing valve, the position illustrated in FIG. 2 in which the valve section R3 is in operation providing for supply of pressure fluid through the valve 16 and discharge of fluid from the motors through the valve 17. By shifting the reversing valve R to bring the valve section R1 into registry with the passages 27-39a and 27a-39, the pressure fluid supplied by the pump 25 will be delivered to the valve 17 and the discharge will occur through valve 16.

The valve R may also have a shut-off position, provided, for example, by the section R2 of the valve, in which position the pressure fluid from the pump 25 will merely be recirculated to reservoir.

In normal operation of the system when the reversing valve R is positioned for either direction of operation, the main control valve is employed for changing the condition of operation from one-motor operation to two-motor operation, or vice versa. The arrangement of the valves 24 and 36 and of the passages and connections associated therewith is such that even during shift of valve 40 from one condition to the other, the motors will not experience a neutral condition tending to result in dropping of the load.

We claim:

I. A fluid control system for power means having first and second hydraulic motors connected to deliver power to a power shift and each of said motors having first and second passages extended from opposite sides thereof for supply and discharge of operating fluid, the control system comprising first and second valve devices each having first and second cavities and a valve seat around a port interconnecting the first and second cavities, the first and second cavities of the first valve device being connected respectively with the first passages of the two motors and the first and second cavities of the second valve device being connected respectively with the second passages of the two motors, and each of said devices having a valve cooperating with said seat and movable to open and close said port, first connection means providing for connection of the first cavity of the first valve device with a source of hydraulic operating fluid, second connection means providing for connection of the first cavity of the second valve device with reservoir, said two valve devices providing for operation of only the first motor when the two valves are closed and for operation of both motors when the two valves are open, each of said valve devices having fluid pressure means for operating the valves including a pressure fluid chamber at that side of the valve acting to move the valve against the valve seat and thereby close the port upon build-up of pressure in said pressure fluid chamber, each valve device having a restricted orifice interconnecting said first cavity thereof and its fluid pressure valve operating chamber, and each valve having a discharge line with a restricted orifice for connecting its fluid pressure valve operating chamber with reservoir.

' 2. A fluid control system as defined in claim 1 and further including a master control valve for opening and closing said discharge lines.

3. A fluid control system as defined in claim 2 and comprising fluid pressure means for shifting said valve between said two positions and comprising a fluid pressure control chamber having a supply connection and a discharge connection, and a controllable valve in one further including a discharge connection for delivering 5 of said connections having two operating positions propressure fluid from the second cavities of said valve devices to reservoir, and means operated by said master valve for opening said discharge connection when the master valve is operated to close the discharge lines from the fluid pressure valve operating chambers.

4. A fluid control system as defined in claim 1 and further including means for inverting the connections with the source of hydraulic operating fluid and with the reservoir so that the first connection means connects the first cavity of the first valve device with reservoir and so that the second connection means connects the first cavity of the second valve device with the source of supply of hydraulic operating fluid, and thereby provides for reverse operation of the motors.

5. A fluid control system for power means having first and second hydraulic motors connected to deliver power to a power shaft and each of said motors having first and second passages extended from opposite sides thereof for supply and discharge of operating fluid, the 25 control system comprising a valve device having first and second cavities and a valve seat around a port interconnecting the first and second cavities, the first and second cavities of the valve device being connected respectively with the first passages of the two motors, and the valve device having a valve cooperating with said seat and movable to open and close said port, first connection means providing for connection of the first cavity of the valve device with a source of hydraulic operating fluid, said valve device providing for supply of op- 35 crating fluid to only the first motor when the valve is closed, and for operation of both motors when the valve is open, the valve device having fluid pressure means for operating its valve including a pressure fluid chamber at that side of the valve acting to move the 4 valve against the valve seat and therebyrclose the port upon build-up of pressure in said pressure fluid chamber, the valve device having a restricted orifice interconnecting said first cavity thereof and its fluid pressure valve operating chamber, and the valve having a discharge line with a restricted orifice for connecting its fluid pressure valve operating chamber with reservoir.

6. A fluid control system for power means having first and second hydraulic motors connected to deliver power to a power shaft and each having passages extended therefrom for supply and discharge of operating fluid, the control system comprising supply and discharge valve means providing alternatively for operation of the first motor only and for operation of both motors, and including a valve adapted in a first position to shut off the fluid with respect to one motor and a second position to establish a fluid flow with respect to both motors, and control mechanism for said valve viding alternatively for build-up and discharge of pressure in said chamber, each of said supply and discharge connections having a restriction therein providing'respectively for retarded build-up and discharge of pres- 0 sure in the control chamber.

7. A fluid control system for power means having first and second hydraulic motors connected to deliver power to a power shaft and each having passages ex tended therefrom for supply and discharge of operating 5 fluid, the control system comprising supply and discharge valve means providing alternatively for operation of the first motor only and for operation of both motors, and including valve chambers respectively connected with the supply passages for the two motors and 0 one of which is a pressure fluid supply chamber, a port between the valve chambers, a control valve for opening and closing said port and thereby provide alternatively for supply of pressure fluid to one motor and to both motors, said valve also having means cooperating with said port to provide metering grooves for restricting flow from the pressure fluid supply chamber to the other chamber during opening and closing movement of the valve, and means for actuating said control valve including a fluid pressure control chamber having a supply connection and a discharge connection, and a manually controllable valve in one of said connections providing alternatively for build-up and discharge of pressure in said chamber, each of said supply and discharge connections having a restriction therein providing respectively for retarded build-up and discharge of pressure in the control chamber.

8-. A fluid control system for power means having a plurality of hydraulic motors connected to deliver 0 power to a power shaft and each of said motors having passages extended therefrom for supply of operating fluid and for discharge of operating fluid to reservoir, the control system comprising supply and discharge valve means providing alternatively for operation of 5 one motor only and for operation of more than one motor, and including a valve adapted in a first position tov shut off the fluid flow with respect to all but one motor and a second position to establish fluid flow with respect to more than one motor, the control system fur- O ther including manually controllable means for effecting movement of said valve between its first position and its second position, and for each motor means providing for discharge of operating fluid from any inactive motor to reservoir independently of the discharge 5 from an active motor, and thus for operation of any inactive motor in the absence of pressure fluid at times when the valve is in its position to shut off fluid flow with respect to more than one motor.

, UNITED STATES PATENT 'OFFICE CERTIFICATE OF CORRECTION Patent No. 3,849,985 'Dated November 26, 1974 Inventor( s) Frank W. Ratliff et a1 It is certified that error appears in the above-identified! patent and that said Letters Patent are hereby corrected as shown below:

- -Col.' 4, Line 3, change '26. 56. to read --36.-'

C01. 6, Line 37, change "shift"'to read' -shat-- Col. 7', Line 35, change "said iralve device" to read thereby-- Signed add sealed this 8th day of April 1975.

(SEAL) Attest: C. MARSHALL DANN RUTH C. ASON Commissioner of Patents Arresting Officer T and Trademarks 1 FORM 904050 USCOMM-DC scan-es IL. GOVIINIEIIT IIIIITING OFFICE I9! O-QSFL 

1. A fluid control system for power means having first and second hydraulic motors connected to deliver power to a power shift and each of said motors having first and second passages extended from opposite sides thereof for supply and discharge of operating fluid, the control system comprising first and second valve devices each having first and second cavities and a valve seat around a port interconnecting the first and second cavities, the first and secOnd cavities of the first valve device being connected respectively with the first passages of the two motors and the first and second cavities of the second valve device being connected respectively with the second passages of the two motors, and each of said devices having a valve cooperating with said seat and movable to open and close said port, first connection means providing for connection of the first cavity of the first valve device with a source of hydraulic operating fluid, second connection means providing for connection of the first cavity of the second valve device with reservoir, said two valve devices providing for operation of only the first motor when the two valves are closed and for operation of both motors when the two valves are open, each of said valve devices having fluid pressure means for operating the valves including a pressure fluid chamber at that side of the valve acting to move the valve against the valve seat and thereby close the port upon build-up of pressure in said pressure fluid chamber, each valve device having a restricted orifice interconnecting said first cavity thereof and its fluid pressure valve operating chamber, and each valve having a discharge line with a restricted orifice for connecting its fluid pressure valve operating chamber with reservoir.
 2. A fluid control system as defined in claim 1 and further including a master control valve for opening and closing said discharge lines.
 3. A fluid control system as defined in claim 2 and further including a discharge connection for delivering pressure fluid from the second cavities of said valve devices to reservoir, and means operated by said master valve for opening said discharge connection when the master valve is operated to close the discharge lines from the fluid pressure valve operating chambers.
 4. A fluid control system as defined in claim 1 and further including means for inverting the connections with the source of hydraulic operating fluid and with the reservoir so that the first connection means connects the first cavity of the first valve device with reservoir and so that the second connection means connects the first cavity of the second valve device with the source of supply of hydraulic operating fluid, and thereby provides for reverse operation of the motors.
 5. A fluid control system for power means having first and second hydraulic motors connected to deliver power to a power shaft and each of said motors having first and second passages extended from opposite sides thereof for supply and discharge of operating fluid, the control system comprising a valve device having first and second cavities and a valve seat around a port interconnecting the first and second cavities, the first and second cavities of the valve device being connected respectively with the first passages of the two motors, and the valve device having a valve cooperating with said seat and movable to open and close said port, first connection means providing for connection of the first cavity of the valve device with a source of hydraulic operating fluid, said valve device providing for supply of operating fluid to only the first motor when the valve is closed, and for operation of both motors when the valve is open, the valve device having fluid pressure means for operating its valve including a pressure fluid chamber at that side of the valve acting to move the valve against the valve seat and thereby close the port upon build-up of pressure in said pressure fluid chamber, the valve device having a restricted orifice interconnecting said first cavity thereof and its fluid pressure valve operating chamber, and the valve having a discharge line with a restricted orifice for connecting its fluid pressure valve operating chamber with reservoir.
 6. A fluid control system for power means having first and second hydraulic motors connected to deliver power to a power shaft and each having passages extended therefrom for supply and discharge of operating fluid, the control systeM comprising supply and discharge valve means providing alternatively for operation of the first motor only and for operation of both motors, and including a valve adapted in a first position to shut off the fluid with respect to one motor and a second position to establish a fluid flow with respect to both motors, and control mechanism for said valve comprising fluid pressure means for shifting said valve between said two positions and comprising a fluid pressure control chamber having a supply connection and a discharge connection, and a controllable valve in one of said connections having two operating positions providing alternatively for build-up and discharge of pressure in said chamber, each of said supply and discharge connections having a restriction therein providing respectively for retarded build-up and discharge of pressure in the control chamber.
 7. A fluid control system for power means having first and second hydraulic motors connected to deliver power to a power shaft and each having passages extended therefrom for supply and discharge of operating fluid, the control system comprising supply and discharge valve means providing alternatively for operation of the first motor only and for operation of both motors, and including valve chambers respectively connected with the supply passages for the two motors and one of which is a pressure fluid supply chamber, a port between the valve chambers, a control valve for opening and closing said port and thereby provide alternatively for supply of pressure fluid to one motor and to both motors, said valve also having means cooperating with said port to provide metering grooves for restricting flow from the pressure fluid supply chamber to the other chamber during opening and closing movement of the valve, and means for actuating said control valve including a fluid pressure control chamber having a supply connection and a discharge connection, and a manually controllable valve in one of said connections providing alternatively for build-up and discharge of pressure in said chamber, each of said supply and discharge connections having a restriction therein providing respectively for retarded build-up and discharge of pressure in the control chamber.
 8. A fluid control system for power means having a plurality of hydraulic motors connected to deliver power to a power shaft and each of said motors having passages extended therefrom for supply of operating fluid and for discharge of operating fluid to reservoir, the control system comprising supply and discharge valve means providing alternatively for operation of one motor only and for operation of more than one motor, and including a valve adapted in a first position to shut off the fluid flow with respect to all but one motor and a second position to establish fluid flow with respect to more than one motor, the control system further including manually controllable means for effecting movement of said valve between its first position and its second position, and for each motor means providing for discharge of operating fluid from any inactive motor to reservoir independently of the discharge from an active motor, and thus for operation of any inactive motor in the absence of pressure fluid at times when the valve is in its position to shut off fluid flow with respect to more than one motor. 